I have been tuning on my BB and am having trouble with the idle mixture. It runs great at idle and off idle, but while idling in my shop it will make your eyes burn (rich). I know it will be rich with this size cam but I was just wondering if the guys with experience with this size solid roller could step in and share your knowledge. Cam spec’s; Lanati solid roller .700 lift int. and exh., duration at .050 254, 112 lobe center, 11 to 1 comp. I have checked the vacuum and Power valve, also checked the transition slots for blade position. Idels at 1100 in N and 900 in D. Timing is around 15 to 25deg at idle (moves around). I can reach in the window and turn the key and it will crank with no problem.

Thanks Neal

 

First step is to get the timing fixed. With a cam that large you need 30 degrees advance at idle and it needs to be steady. Once you have that you should be able to lean the idle mixture out some.

Note that advance needs to be no more than 36 dgr at high rpm WOT so you need to modify the advance curve (limit the slots) until it gives you the curve you need. If it is a street car you want some vacuum advance. About 10 dgr. In that case you can hook the vacuum can to manifold vacuum and lower your static timing to 20 dgr at idle (with the vacuum advance you get back to 30 @ idle).

 

I am going to install the heavier springs and possibly lighter weights to try and settle the idle timing down some. I have it set at around 20° without vacuum advance, with the vacuum advance it is around 30° to 32°.

Thanks for the input Zwede, I'll get on this tomorrow and see if I can get the timing to settle down.

Neal

 

Well I found a few things that were contributing to my problems, first one of the weights were stuck in the distributor once I got it off the shaft I was able to free it up and get it to work. I than installed some light weights and stronger springs this steadied the idle timing down were I could set it. Its set at 18° static and this gives me 30° with vacuum advance connected. When I hit the gas and bring the RPM’s up I have way too much total timing, I will have to limit the centrifugal advance. I know I have seen this procedure explained somewhere on here I will try and find it.

I am thinking of purchasing an exhaust gas analyzer from Northern Tools, it’s hard to get everything just right without hard data. While I was working on the timing and carb adjustments I could tell it was getting a lot better its just hard to get the perfect setting with your nose. I also have some A/F meters to install to monitor the conditions while driving.

Neal

 

Be sure you are checking the high rpm advance with the vacuum can disconnected. With it connected it is normal to see high 40's, even 50 dgr. But disconnect it and see what your max timing is. If it is more than 36 you need to shorten the advance slots. Easiest is to weld the slots and then grind them back out until you get ~36.

 

Forgot about that, I was checking with the vacuum advance connected. I will have to check that out tommorrow, I didn't have any help today I will have to round some help up for tommorrow to try and get a feel of what RPM all the timing is in at, gota go to work now.

Thanks for the ifno, Neal

 

I have only used two types of distributers on my solid roller motors in the past 18 years. The Mallory Unilite with a Crane adjustable vacuum advance which I had recourved by mallory. They set it as per my request for 16 degrees of mech advance and all in by 3000 rpm.

My heads only required about 34 degrees total without vacuum advance.

so I could set it at 18 at idle and 16 mech and be right on.

Your vacuum should be on a ported vacuum so you will not have any vac. advance until the throttle blades open.

 

I somewhat agree on the ported vacuum, the extra advance at idle helps when you put it in gear. The idle can be set lower and you can use a tighter converter with large cam shafts.

I'll try and make this dist work (Accel HEI), if I can't I'll pickup one up that is allready setup. Thats one of the things I like about this car, I have worked on every inch of it myself and with the help of this forum have just about got it the way it needs to be.

My Holley 1000 HP has no ported vacuum.

Neal

 

Once your get the ignition 100% the next thing is the carb. I've been using Demons, but the problems are the same. You need to adjust the four corner idle mix screws with a vacuum gauge or better yet a tail pipe sniffer.

I ended up drilling my throttle blades to lean the idle out.

 

Would you recomend the mallory unilite most everyone runs an MSD,
I would like to have a mallory just to be different as long as it
will not give me a headache.

 

This is opposite to what I always do. I like heavy weights and light springs to bring the advance curve in faster. You want it all in by 3000 rpm.
I also shorten the advance slot.
I had alot of wandering with the timing with my unilite distributor and eventually went to a MSD timing computer. It used electronics to give you a set curve all in by 3000. It makes for a very steady timing curve repeatable time and time again.
I too like to drill the throttle plates along with putting a .015 wire in each of the idle circuits. This is recommended by holley for any healthy cam.
I idle screws should be very close to 1 1/2 turns out from bottoming.
Set properly your car will idle in the garage without burning your eyes.

 

I bought my Mallory unilite probably not long after they came out in the late 80's. Vastly superior to a GM hei when used in conjuntion with a quality coil like a MSD Blaster and good wires and plugs.

Only one time did it ever fail. The modual would not send a spark whenever the motor really got hot. I put 100,000 Vette miles on it and today it's running in a 65 Nova drag car. Mallory recourved it several times to match ideas of mine over the years. I would very the what rpm the advance would start, how much total , and when all the advance was in.

I always kept where the all in was right around 3000 - 3200 to match my highway cruise rpm. Right at 85-90 mph in OD where i spent most of my time driving. I did try some really fast ignition courves where you had all in at 2500 or 2800 rpm and it always ended up being way to much timing too early. It's very easy to see the HP loss on a rear wheel dyno. Thats how you get very little low rpm hp and then a really fast climb to the top.

Just to be different and try something new I bought the MSD digital so I could with the flip of a dial change my ignition courve and total advance. Crane Cams also came out with a simular distributer. My MSD is just an expensive toy that doesn't run any better than my old Mallory

My motors have always just fired up in an instant with or without a multi spark unit attached. I use a Crane digital Multi spark and it doesn't run any better or worse in multi spark mode under 3000 or so rpm. I just use it for a sequential two stage rev limiter

 

Thanks I have been wondering if an optical trigger would be a good way to go and if the infrared light beam might be a problem, if you
have had almost no problems in over 20 yrs with one thats good
enough for me, I was having a hard time trying to decide between
optical or magnetic for a dist.

 

Ive had problems with Mallory unilites and Hyfire units,went with Msd and no more problems.

 

Yep once I geet the timing worked out I will start on the carb. the idle screws are all right at 1 turn out, turn them in and the motor will die, turn them out and the motor will load up so I do have control or the motor with the idle circut.
I have two A/F meters (some I made myself) that I am going to install, I am also thinking of ordering an exhaust gas analyzer. Not sure wihich will be better.

Neal

 

Norval the timing at idle was all over the place, the car idles at 1100 RPM's, timing was coming in at this point so to stabilize the timing I installed the heavier springs once I get the slots fixed to limit the total timing I will toy with the springs, I need them heavy enough to hold the timing at idle but light enough to allow all in by 3000 rpm's.
Once the timing is correct I will start on the carb, the idle screws are right at 1 turn out so I think I am close, or would you recommend getting them out to 1 1/2 turns?

Neal

 

Turn them out till you get the highest idle or vacumn

 

Well I had time to work some on the timing today, I disconnected the vacuum advance per Zewed’s instructions and set the initial at 16° to 18° (this gives me 28° to 30° at idle with the vacuum advance connected), this gave me right at 36° to 38° total. I didn’t have any help so I am not sure on the RPM’s to reach total, I will check that out when I can get some help. The idle is set at 1100 RPM’s, the timing starts advancing right at this point, so It looks like this will be the lightest springs I can use (I may look into a timing computer so I can adjust the all in point to were I need it, if it’s to far off). Once I get an idea of were the all in point is I can move on the carb tuning, first step will be to install the O2 sensors so I can see what’s going on with the mixture.

Neal